<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>注册页面</h1>
<form action="">
    <input type="text" name="username" placeholder="用户名" onblur="fn()">
    <span></span><br>
    <input type="text" name="password" placeholder="密码">
    <input type="button" value="注册">
</form>
<!--引入axios框架-->
<script src="https://cdn.bootcdn.net/ajax/libs/axios/0.21.1/axios.min.js"></script>
<script>
function fn() {
    //alert("编辑完成!");
    //得到form表单中的数据
    let data=new FormData(document.querySelector("form"));
    //发出异步请求
    axios.post("/check",data).then(function (response) {
    let  span=document.querySelector("span");
    span.innerText=response.data;
    })
}
</script>
</body>
</html>